[v4,14/33] migration/multifd: Make multifd_send() thread safe

Commit Message

Maciej S. Szmigiero Jan. 30, 2025, 10:08 a.m. UTC

From: "Maciej S. Szmigiero" <[e-mail]>

multifd_send() function is currently not thread safe, make it thread safe
by holding a lock during its execution.

This way it will be possible to safely call it concurrently from multiple
threads.

Reviewed-by: Peter Xu <[e-mail]>
Signed-off-by: Maciej S. Szmigiero <[e-mail]>
---
 migration/multifd.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Patch

diff --git a/migration/multifd.c b/migration/multifd.c
index 810e7b1fb340..02d163fe292d 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -50,6 +50,10 @@  typedef struct {
 
 struct {
     MultiFDSendParams *params;
+
+    /* multifd_send() body is not thread safe, needs serialization */
+    QemuMutex multifd_send_mutex;
+
     /*
      * Global number of generated multifd packets.
      *
@@ -339,6 +343,8 @@  bool multifd_send(MultiFDSendData **send_data)
         return false;
     }
 
+    QEMU_LOCK_GUARD(&multifd_send_state->multifd_send_mutex);
+
     /* We wait here, until at least one channel is ready */
     qemu_sem_wait(&multifd_send_state->channels_ready);
 
@@ -507,6 +513,7 @@  static void multifd_send_cleanup_state(void)
     socket_cleanup_outgoing_migration();
     qemu_sem_destroy(&multifd_send_state->channels_created);
     qemu_sem_destroy(&multifd_send_state->channels_ready);
+    qemu_mutex_destroy(&multifd_send_state->multifd_send_mutex);
     g_free(multifd_send_state->params);
     multifd_send_state->params = NULL;
     g_free(multifd_send_state);
@@ -857,6 +864,7 @@  bool multifd_send_setup(void)
     thread_count = migrate_multifd_channels();
     multifd_send_state = g_malloc0(sizeof(*multifd_send_state));
     multifd_send_state->params = g_new0(MultiFDSendParams, thread_count);
+    qemu_mutex_init(&multifd_send_state->multifd_send_mutex);
     qemu_sem_init(&multifd_send_state->channels_created, 0);
     qemu_sem_init(&multifd_send_state->channels_ready, 0);
     qatomic_set(&multifd_send_state->exiting, 0);